This project will test for the presence of several viral antibodies in adult and juvenile Macacas on Cayo Santiago, Puerto Rico. This has been a closed colony of Rhesus monkeys since 1938. A serological screen carried out in the early 1950's indicated the presence of antibody to SV 40 (46%), herpes B (27%) and measles virus (80%) of the animals in the colony. The objective will be to determine after some 40 years as a closed colony, if herd immunity to the three previously studied antigens has been lost and would, therefore, provide an animal population useful for the testing of related strains of viruses. Three other antigens are also included in the screen. They are: rhesus CMV, simian retrovirus D (SRV-I) and simian T-lymphotropic virus type III (STLV-III). If this colony is shown to be serologically negative for these other three simian viruses, then animals from this colony could be used in the study of these simian diseases as models for related human diseases. With the tremendous interest and need for animal models of AIDS, we have added the following viral antigens to our testing protocol: human T-lymphotropic virus I (HTLV-I) and human immunodeficiency virus (HIV). In addition, we have broadened the scope of our testing to include animals in the NINCDS breeding colony in Puerto Rico. Animals shown to be serologically negative for antibodies to the added retroviral antigens are urgently needed for studies in AIDS.